Salmon Life Cycle

Salmon Life Cycle. Outline of each stage in the
life of a Pacific salmon, from roe to adult salmon to dying salmon kelt. Includes
our video of leaping Coho salmon in the Olympic National Park of the Pacific
Northwest.

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A
salmon’s life cycle might span up to 7 or more years.

It starts far inland in
shallow gravel-bed streams and ends in the very same stream where it all began.

In the intervening years, a Pacific salmon embarks on a lengthy salt water
odyssey throughout Pacific Ocean.

The newly fertilized eggs sink to the gravel. The
female then swims upstream and sweeps and slaps the bottom of the stream in
order to stir up the silt and gravel.

The silt and gravel will drift and settle
over the eggs to protect them until they hatch within 2-6 months. In this
fashion the female creates her nest, called a redd, which might end up measuring anywhere from 2 – 10 feet long
and 1 – 6 feet wide.

A redd might hold up to 1,200 eggs, and a single salmon
female might dig 7 redds.

20% of the eggs might survive beyond the alevin stage
to become fry.

Alevin,
or yolk-sac fry

Alevin are brand-new
hatchlings with egg yolk sacs still attached. Alevin remain hidden in the
gravel subsisting on the egg yolk on its belly. This stage in a salmon’s life
ends when the egg yolk and sac are absorbed, approximately 24 hours.

Fry

Hatchlings
that have used up and absorbed the yolk are called fry. The tiny fry have used up the yolk sac. and leave the gravel to find their own food. They subsist on plankton. At this stage of the salmon life cycle they look
a lot more like tiny fish.

Some
of the newly hatched fry will remain in the freshwater creek for a
few weeks (pink and chum salmon), while Sockeye salmon hang out in the creek
for 1-3 years before leaving the stream and migrating toward the ocean.

Parr
are mottled silvery juvenile salmon still living in freshwater streams. They
are highly camouflaged with patterns of bars and spots on their sides.

Smolt

Smolt
are juvenile salmon living in brackish river estuaries near saltwater or in the
mouths of the rivers. Their bodies must undergo the physiologic changes, called
“smoltification,” that will allow them to live in the ocean.

Smoltification may
take from weeks to months, depending on the species. Smolt are approximately 15-20
cm (7.5”) long. They lose their mottled camouflage and are silver when they finally
head to sea.

(Below:
Coho salmon smolt. There are only remnants of the parr striped mottling visible
in its skin. This will soon disappear altogether. Image by Flickr user patricksensei- Creative Commons)

At
a certain point of maturity, their bodies tell them it’s time to return back to
the very stream where they hatched as alevin.

Once
the salmon begin their return trek to freshwater in order to spawn, hormonal
changes trigger physical changes in the salmon, depending on the species.

Depending on species, males develop a
hooked mouth (a kype), sharp canine
teeth, a bulge or a hump in front of the dorsal fin, and color changes.
These changes are important not only for reproduction but also to equip the male to protect
its females.

The changes in the
females are much less pronounced, however their color does change.

Salmon stop eating
once they commence the return to sweet water to spawn. The use of their
red muscles through jumping and strenuously moving upstream against the
current causes a shift of the red muscle pigment into other areas of their
body, including the skin.

How do salmon
manage to get back to their birth stream?

A remarkable feature of the salmon life cycle is a salmon's ability to navigate its way thousands of miles through the Pacific Ocean,
and then when sexually mature, to home in on the exact stream where it was born up to 7 years previously, in order to spawn.

Spawning
salmon are drawn inexorably to their natal spawning grounds. As the
multitudes of spawning salmon converge on their respective rivers and creeks,
the event is called a salmon run. Salmon runs occur every year, depending upon
the species of salmon.

Males
and females pair up. The male works hard to protect the female. Some species
have grown huge canine teeth with which to ensure his success in spawning.

In the shallow water of a gravelly stream bed, the
female ‘cleans’ the stream bed and then lays her eggs (roe) at the same time as the male releases milky sperm, called milt, over the eggs.

The salmon life cycle will start over with the next generation of salmon over the following few months.

(Below:
Salmon female is digging her redd by slapping the gravel with her tail. Image by Flickr user soggydan- Creative Commons)

Salmon
that have completed their spawning ritual are known as kelt. Kelts look tattered and trashed. Spawning triggers “programmed
senescence,” or rapid aging and deterioration due to the completion of spawning, the lack of
eating, and the drain of corticosteroids in their bodies.

For every species
of Pacific Salmon, both males and
females, spawning marks the last event of their lives. Their immune
system and organs fail rapidly, and the exhausted kelts die within a few
days to a week of spawning. None survive to spawn another day.

The nourishment supplied by their decaying bodies
will return to both land and water and become available to the hatching fry, and to every
other species, both flora and fauna, within the riparian environment of the
stream.

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